A starglass is simply a mirror. This is what mirrors were called in the time of the Befores, and the only people who still use this term are the citizens of Overvale, a remote and isolated village in the Atlica Mountains. There, reflections are outlawed, and only one starglass remains, which is heavily protected by the village council. It is used as a tool of control and obedience, and only those citizens who prove themselves worthy by abiding by the laws of the village will ever get to gaze upon it.
Use in Magic
Starglasses were often utilized by mages to travel across the Ethereal Plane. They acted as portals, and a spellcaster could enter and exit any starglass or reflective surface large enough to accommodate their physical form. This was the limitation, although there were some mages powerful enough to transmute themselves into smaller forms, or use a small familiar to carry out some task. This remained the biggest limitation until the creation of the wraighs, a creature made of etheral shadow, who could enter and exit any reflective surface, regardless of size. This is because they do not have material bodies. The other drawback to using a starglass for this type of teleportation was that the starglass could be physically broken.